In recent years, in a mobile communication network, attention has been focused on a multicast technique in which data are simultaneously distributed only to plural specific radio terminals. In a network called the Universal Mobile Telecommunication System (UMTS) based on the 3GPP (The 3rd Generation Partnership Project), a contents-distributing service called the Multimedia Broadcast and Multicast Service (MBMS) is supported for providing multimedia broadcasting and broadcast services. Further, discussions have been under way so that the Long Term Evolution (LTE) also supports the MBMS (Non-patent Document 1). According to the standard specification of 3GPP, any types of base stations (for example, macro base station and micro base station) can support the MBMS.
The radio terminal can receive multicast signals or broadcast signals of MBMS data regardless of whether the radio terminal is in an active state or an idle state, which means a standby state. Further, at the time when the radio terminal moves to other cells while receiving the MBMS data, the cell reselection, cell update or handover is implemented depending on communication states of the radio terminal. When in the idle state, the radio terminal receives paging information by using a paging channel (PCCH) from a radio base station to which the radio terminal serves, and checks whether any incoming calling exists or not on the basis of the paging information. The term cell reselection refers to an operation that changes a base station (current serving destination to which the radio terminal serves) that transmits the paging information, to the other base station (other serving destination to which the radio terminal serves). When in the active state, the radio terminal establishes synchronization with the base station to which the radio terminal serves to receive and transmit user data. The term handover refers to an operation that changes the base station to which the radio terminal serves, to the other base station, due to the fact that the radio terminal in the active state moves.
In the UMTS and the LTE of 3GPP, in addition to the macro base station, a femto base station (also called “home base station”) is defined as an inexpensive, small base station having limited performance (see Non-patent Document 2 and Non-patent Document 3). The general femto base station is a small base station located indoors and connected with the existing broadband line. Through the broadband line, the general femto base station accesses to the communication network to carry out communication.
As related art documents in connection with the 3GPP, Non-patent Documents 1 through 3 listed below are given for example.